The use of network based electronic communications and information processing systems for information control and information retrieval has rapidly proliferated in modern business environments. Within a typical enterprise, hundreds of client computer systems and server computer systems are constantly accessed by hundreds, or even thousands, of users for obtaining company information, news, competitive information, training materials, and the like, via one or more company wide LANs (local area networks) or WANs (wide area networks), or via the networked resources of the vast communications network known as the Internet.
Generally, digital communications networks (e.g., LANs, WANs, the Internet, etc.) are packet switched digital communications networks. As used generally, the term network refers to a system that transmits any combination of voice, video and/or data between users. The network includes the underlying architecture of connected clients and servers and their associated software (e.g., network operating system in the client and server machines, the cables connecting them and the supporting hardware, such as hubs, switches, routers, etc.). Packet switching refers to subdividing data comprising a message into a number of smaller units of data, or packets, and routing the packets individually through a number of nodes of the communications network.
The nodes of the digital communications network are generally made up of servers, clients, NOS (network operating system) services and supporting hardware. Servers are typically high-speed computer systems that hold programs and data or perform services that are shared by network users (e.g., the clients). The clients (e.g., desktop computer systems, workstations, and the like) are typically used to perform individualized, stand-alone processing and access the network servers as required. The actual communications path hardware is the cable (twisted pair, coax, optical fiber) that interconnects each network adapter. In wireless systems such as WLANs (wireless LANs) and the like, antennas, access point devices, and towers are also part of the network hardware.
Data communications within a network is generally managed by a one of a number of protocols such as, for example, TCP/IP, IPX, or the like. The physical transmission of data is typically performed by the access method (Ethernet, Token Ring, etc.) which is implemented in the network adapters that are plugged into the computer systems. The standardized communications protocols enable the widespread interoperability of communications networks and the widespread exchange of business related information.
In a large enterprise network or on the Internet, the Internet Protocol (IP) is used to route the packets among the various nodes or from network to network. Routers contain routing tables that move the datagrams (e.g., frames, packets, or the like) to the next “hop”, which is either the destination network or another router. In this manner, packets can traverse several routers within an enterprise and a number of routers over the Internet.
Routers inspect the network portion (net ID) of the address and direct the incoming datagrams to the appropriate outgoing port for the next hop. Routers move packets from one hop to the next as they have routing information to indicate the most efficient path that a packet should take to reach it's destination. Eventually, if the routing tables are correctly updated, the packets reach their destination. Routers use routing protocols to obtain current routing information about the networks and hosts that are directly connected to them.
In a manner similar to routers, many modern switches now include routing functionality. Such routing switches, as with routers, function by forwarding data packets from one local area network (LAN) or wide area network (WAN) to another. Based on routing tables and routing protocols, switches/routers read the network address in each transmitted frame and make a decision on how to send it based on the most expedient route (traffic load, line costs, speed, bad lines, etc.). These network addresses include both a MAC address (media access control address) and an IP address (Internet protocol address).
The routing tables are indexed with respect to the addresses of the various nodes of the communications network. These addresses are used to route the packets to the required destination. Since each component on the network has its address, the resulting address space can be extremely large and unwieldy. Large data spaces can be difficult to work with within high-speed router/switches. The problem is even more pronounced with the routers operating at the core of the extremely large networks many enterprises are building, and with routers functioning near the core of the Internet. The resulting address space can span many hundreds of megabytes of memory. To manage the large address space, many prior art address space hashing schemes have been developed.
Address space hashing has become a widely used method to reduce the huge addressing space of a large network to a small, relatively inexpensive, memory table. Due to the fact that the majority of installed networks are based upon Ethernet protocols, many different types of Ethernet MAC address hashing-based address handling methods have been implemented. For example, when a packet arrives at a switch or router, it will need a destination address (DA) lookup to forward the packet, and possibly also a source address (SA) lookup to learn or authenticate the sending station. The network addresses will be used to generate hashing pointers, which are normally around 10–20 bits depending on table size.
The hashing pointer is generated using a hash function, wherein a hash function H can be described as a transformation that takes a variable-size input m (e.g., 48-bit MAC SA/DA), and a variable-size key k, and returns a fixed-size hash value “h” (e.g., hashing pointer), h=H(m, k). Each hashing pointer references a block of memory containing one or multiple MAC entries. Each entry stores the whole 48-bit MAC address and a switching tag related to this address. This entry contains information such as the next-hop forwarding data (the switch port(s) to forward the packet to, destination MAC address, destination VLAN, etc.), packet priority, etc.
When table referencing happens, the MAC address/addresses from the valid entry/entries under the hashing pointer will be compared against the original MAC address and a hit/miss or known/unknown decision will be made accordingly for the DA or SA lookup. Any further decisions based upon forwarding/learning etc., will be made based on the table search results and system setup. The goal of the system is to reduce the address size from a very large block (e.g., 48 bits or more) to a smaller more manageable block (e.g., 10–20 bits), while avoiding address aliasing, where two or more addresses generate a common hash pointer (e.g., a conflict or collision).
Hashing conflicts/collisions have a very adverse effect on the performance of the network router/switch. The hardware of the router/switch is optimized to perform the hashing address space translation very rapidly. In the event of a collision, either a new hash pointer is computed with a different key k (which consumes additional memory bandwidth) or a software based error handling routine is used to resolve the address aliasing. The software based routines execute much more slowly than the normal forwarding hardware. Thus, it becomes critical to network performance that the switch/router implement a fast and efficient address space hashing table.
One prior art solution to this problem involves use of an exceptionally large hashing pointer. For example, for a 48-bit input, a 24-bit hashing pointer can be implemented as opposed to, for example, a smaller 10-bit hashing pointer. The 24-bit hashing pointer reduces the likelihood of collisions as addresses are transformed from 48 to 24-bits as opposed to 48 to 10-bits. Unfortunately, the 24-bit hashing pointer results in a larger routing table (e.g., 224 number of entries) which requires more memory and hence increases cost.
Another prior art solution is the use of a sophisticated hashing function for resolving the hash pointer. For example, a sophisticated hashing function can be designed to use each and every bit of a 48-bit input to generate a resulting 10–12-bit hashing pointer. The function can be configured to give a very high likelihood of different addresses transforming to different hashing pointers. Unfortunately, sophisticated and overly complicated hashing functions can be very difficult to implement in hardware. This can be even more problematic when the switch/router is designed to function at high-speed, wherein table lookups and routing decisions have to be made within a very small number of clock cycles.
Both of the above prior art solutions are increasingly outmoded, as the address spaces which are required to be efficiently indexed and tabled grow increasingly large. For example, newer versions of the Internet protocol (e.g., IPv6) will use 128-bit IP addresses. Thus, prior art type sophisticated hashing functions designed to use each and every bit of a 128-bit input to generate a hashing pointer become extremely difficult to implement using high-speed hardware. Similarly, prior art techniques using relatively large hashing pointers with respect to a 128-bit input require too much memory to implement cost-effectively.
Thus, the prior art is problematic in that conventional address space hashing schemes have difficulty scaling efficiently to large address spaces. Prior art address space hashing schemes have difficulty transforming input addresses into hashing pointers at high speed without increasing the number of conflicts/collisions which occur. Additionally, prior art address space hashing schemes that may have sufficient conflict/collision performance are difficult to efficiently implement in high-speed hardware. The present invention provides a novel solution to these problems.